Soil Phosphorous, Potassium and Micronutrients

Transcription

1 Soil Phosphorous, Potassium and Micronutrients

2 Introduction Phosphorous is second only to N in importance for the productivity and health of ecosystems P is scarce in most ecosystems Excessive application of P fertilizers can lead to eutrophication of water supplies

3 Introduction Potassium is abundant in most soils Most is tied up and unavailable to plants K is required by plants in large amounts 9 of the 18 elements essential for plant growth are required in very small amounts Called micronutrients or trace elements

4 Phosphorous in Soils Phosphorous not abundant in natural ecosystems Amounts usually adequate for sustained plant growth as all P taken up by plant is returned to soil in residue P in agricultural systems not sustainable for continued growth Plants are harvested, P not returned to soil in residue in sufficient quantities

5 Phosphorous Balance in Adjacent Watersheds Precipitation.14 Precipitation.14 ' Stream.3 --< nmoff 1 Corn litrer 35 Stream runoff J Wcarhcring Inorganic P 275 kg/ha Weathering Inorganic P Fertilizer JO 976 kg/ha Removed in ,,1 harvest Forested watershed AgricuJtural watershed

6 Phosphorous in Soils In agricultural systems additional P is applied as manure, fertilizer etc. After fertilization, many soils have more P than can be used by the crop Runoff, leaching and erosion may move this excess P into waterbodies triggering eutrophication

7 Eutroph ication Accumulation of Phosphorous in bodies of water Stimulates algae and aquatic plant growth Decaying of plant matter uses up dissolved oxygen in the water resulting in fish die off

8 Fish kill as a result of eutrophication-anoxic condition resulting from the decay of masses of algae whose growth was stimulated by excessive Phosphorous

9 Phosphorous in Soils Where P is deficient land degradation may occur Common in parts of Africa where soils have been mined of P for years.as result of subsistence farming Plants grow sparsely and poorly, land becomes subject to erosion {wind and water) for lack of cover P deficiency indirectly causes N deficiency low P inhibits effective nodulation of legumes

10 African Corn Field Showing Extreme Phosphorous Deficiency

11 Practical Management of P in Soils 1. Choose fertilizer to fit P status of soil This can change over time, so as P availability increases, fertilizer should be reduced 2. Placement of P fertilizers Localized placement in root zone reduces amount needed and reduces potential for P reactions and/or fixation 3. Use fertilizers containing ammonium and P Increases uptake of P, especially in alkaline soils

12 Practical Management of Pin Soils 4. Cycle organic matter Increases plant available Pas organic materials decompose 5. Control soil ph P uptake optimized between ph 6 and 7 6. Enhance mycorrhizal symbiosis May need to innoculate seedlings 7. Choose P-efficient plants

13 Practical Management of P in Soils 8. Reduce runoff and sediment losses Use conservation practices, cover crops, residues etc. Encourage water movement into soil rather than off it 9. Capture excess P before it enters waterbodies Natural or constructed wetlands help tie up P

14 Potassium in Soils Potassium (K) present in soil solution only as positively charged cation -- K + Behavior in soil influenced primarily by cation exchange properties mineral weathering Does not cause offsite environmental problems or toxicity to plants

15 Potassium in Soils K found in high levels in most soils except those dominated by quartz sands Quantity held in exchangeable form at any time is small Most K held as part of primary mineral structure or fixed in forms unavailable to plants K is easily lost by leaching More readily leached in acid than limed soil Attraction of K + to negatively charged colloids slows leaching in limed soils

16 How Liming an Acid Soil can Reduce Leaching Losses of Potassium Acid soil Limed soil K + ions can more easily replace ca2 + ions on the soil colloid in limed soil than they can Al3 + ions in an (unlimed) acid soil H A Ca Al -- Al -- - H Al AJ Ca 2+

17 Potassium in Soils Plants can take up very large amounts of K If K is present in sufficient quantities plants will take up more than they need Termed luxury consumption If plant residues are not returned to the soil luxury consumption can reduce plant available K levels dramatically

18 Relationship Between Available Potassium Levels in Soils, Plant Growth and Plant Uptake of Potassium High ============== Relative plant growth Potassium content of plants t w.. low High Potassium available in soil

19 Practical Potassium Management 1. Understand the sources of gains and losses of available potassium and of factors affecting them Relative importance of each source will vary among soils 2. Realize that soils can supply most of the K required for a natural ecosystem Must supplement where crops are removed

20 Practical Potassium Management 3. Avoid highly acid soils that permit extensive losses of potassium 4. Recycle as much plant absorbed K to soil as possible 5. When needed apply fertilizer in light applications On an annual basis is best

21 Typical Ga.ins and Losses of Available Soil Potassium in a Field System Plant residues Anin1al n1anurcs Con1rncrci ell f ('rtilizcrs Slo\vty availabl'c pot,assi1nu rnincrals Available soil potassitnn Plant removal leaching loss ts Eros1ion losses fixation

22 M icronutrients As important as macronutrients Required in much smaller amounts All can be found in igneous rocks Organic matter an important secondary source for many micronutrients Deficiencies likely to occur where total nutrient contents are low Highly leached, acid soils and organic soils usually deficient

23 M icronutrients Cation micronutrients include Iron, Zinc, Manganese, Copper, Cobalt, Nickel Most are soluble and plant available under acid conditions Can be toxic in very acid soils Deficiencies more common in calcareous soils ph of 6-7 allows sufficient solubility for plants without being toxic

24 Micron utrients Anion micronutrients include Boron, Molybdenum, Chlorine Chlorine usually available in sufficient quantities Can be present in toxic amounts in saline soils Boron commonly most deficient of micronutrients Availability related to soil ph, most available in acid soils Molybdenum availability is increased with increasing ph Liming acid soils will increase the availability

25 (P) commonly is one of the most limiting nutrients for crops and forage. The primary role of P in plants is storage and transfer of energy produced by photosynthesis for growth and reproductive processes. Phosphorus cycles in soil through various processes and in various forms. Some forms are readily available for plant use, and some are not (fig. 1). Adequate P levels promote fruit, flower, and seed production; increase crop yields; promote root growth and hardiness of plants in winter; stimulate tillering; and hasten crop maturity. Phosphate soil tests assist in determining the P cycling in soils, production potential, appropriate P levels for soil microbial processes, and potential crop response to P fertilizer. Moderate levels of P typically are adequate for productivity and soil microbial processes. High levels indicate excessive application of P fertilizer; a potential for loss of soluble P in surface runoff, drainage tile, and groundwater at a shallow depth; and a potential for leaching of P in sandy and organic soils. Figure 1. Soil phosphorus cycle (Pierzinski and others, 1994). Inherent Factors Affecting Soil Phosphorus Inherent soil properties and climate affect the growth of crops and their response to applied P fertilizer and regulate the processes that can restrict the availability of P. Climatic conditions, such as rainfall and air temperature, and site conditions, such as soil moisture and aeration (oxygen level) and salinity (salt content/electrical conductivity) affect the rate of mineralization of P as a result of decomposition of organic matter. Organic matter decomposes, releasing P, more quickly in warm, humid climates than in cool, dry climates. Phosphorus Page 1 Guides for Educators (May 214)

26 Soil Health Phosphorus USDA-NRCS is released faster from well-aerated soils (higher oxygen level) than from saturated soils (lower oxygen level). Soil ph of 6 to 7.5 is ideal for the availability of P for plant use. Values of less than 5.5 and 7.5 to 8.5 limit availability of P as a result of fixation by aluminum, iron, or calcium (fig. 2), which commonly are associated with soil parent material. Moderate levels of P do not readily leach out of the root zone in most soils. Potential for loss of P in these soils is associated mainly with erosion and runoff. Soils that have a high level of P are prone to loss of soluble P in surface runoff, drainage tile, and groundwater at a shallow depth, and sandy and organic soils are prone to loss of P through leaching. To minimize sedimentation and loss of soluble P, closely manage soils that have a high or very The availability of P can be increased by applying lime to acid soils, using practices that increase organic matter, and properly placing P fertilizer, which affects the efficiency of use by crops. Loss of P can be minimized by limiting erosion and runoff, injecting or incorporating P, and limiting or eliminating applications of P fertilizer if the level of P in the soil is high or very high. Adequate P is essential for crop and forage production. It encourages vigorous root and shoot growth, promotes early maturity, promotes efficient use of water by plants, and increases grain yields. Phosphorus deficiency reduces yields by delaying maturity, stunting growth, and restricting energy use by plants. Soil P is relatively stable; it moves very little as compared to nitrogen, unless it is present in excessive amounts. The lack of mobility and low solubility limit the availability of P applied in fertilizer because it is fixed by P compounds in the soil. Fixed P slowly becomes available to crops over several years, depending on the Phosphorus Management high level of P, are subject to erosion and runoff, or are in close proximity to streams, lakes, and other bodies of water. Figure 2. Phosphorus availability across ph ranges (California Fertilizer Association, 1995). type of soil and P compounds (fig. 1). Phosphorus in eroded sediment in bodies of water is also released over several years. Purple leaf tissue is symptomatic of P deficiency (fig. 3). It appears first on the tips of leaves and progresses until the entire leaf exhibits a purple color. Lower leaves die when phosphorus deficiency is severe, especially if hot, dry, windy conditions persist. Emerging leaves commonly are green because plants mobilize available P to the youngest leaves first. Symptoms of P deficiency commonly occur as young plants are exposed to cool, wet conditions. Under these conditions, plant growth exceeds the ability of the roots to supply P. Young plants are especially vulnerable because their root systems are limited and P is immobile in the soil. Cultural or environmental factors that limit root growth contribute to the symptoms of P deficiency. These factors include cool temperatures, wet or dry conditions, compaction of the soil, Page 2 Guides for Educators (May 214)

27 Soil Health Phosphorus damage from herbicide use, damage from insects, salinity, and root pruning from sidedressing knives or cultivators. Once growing conditions become favorable again and further root growth occurs, leaves normally regain their green color. Figure 3. Phosphorus-deficient corn characterized by purple color on lower leaves. The availability of P is controlled by three primary factors soil ph and mineralogy, content of organic matter, and placement of P fertilizer. Lime should be applied to acid soils to achieve an ideal ph level (ph of 6 to 7). Low soil ph severely limits the availability of P for plant use. Soil ph of less than 5.5 typically limits the availability of P by 3 percent or more. Acidity also reduces root growth, which is critical for the uptake of P. High amounts of iron oxides, available aluminum, or calcium carbonates or sulfates in soil fix P, limiting its availability. USDA-NRCS Maintaining the content of organic matter in the soil is important for controlling the availability of P. Mineralization of organic matter provides a significant portion of the P available for crop use. Phosphorus fertilizer and manure or other organic amendments can be applied to remedy P deficiency, but careful management is needed to provide a form of P that is available for plant use. Roots must come in contact with available P for uptake to occur. It commonly is recommended to apply P in the rows as a starter fertilizer to increase early growth, even if the amount of P in the soil is sufficient for grain. Phosphorus can also be injected 2 inches below the seeds of row crops, which provides a ready source of P for young seedlings. Producers should carefully evaluate the value of applying P fertilizer early in the growing season. Seedlings may look better if starter P fertilizer is applied, but yields may not be increased. Primary P management strategies: 1. Apply lime to acid soils to increase ph to between 6.5 and 7. (fig. 2). 2. Apply small amounts of P fertilizer frequently rather than large amounts all at one time. 3. Minimize the tie-up of P by banding or injecting P fertilizer or liquid manure. 4. Place P fertilizer near rows or in furrows, where roots are most active. Page 3 Guides for Educators (May 214)

28 Soil Health Phosphorus USDA-NRCS Measuring Soil Phosphate (PO 4 ) Materials needed to measure phosphate: Plastic container and probe for gathering and mixing soil samples Phosphate test strips 1/8-cup (29.5 ml) measuring scoop Calibrated 12-mL vial with lid for shaking Squirt bottle Distilled water or rainwater Pen, field notebook, permanent marker, and resealable plastic bags Considerations: Electrical conductivity (EC) should always be measured on a sample before measuring phosphate. Soil nitrate/nitrite and soil ph can also be measured on the sample using the steps in the following paragraphs. Soil P tests, which help in determining potential crop growth and recommendations for fertilizer, are of value only if correlated and calibrated to the response of crops to applied P. Thus, soil P test results are an index of relative availability. Quick in-field hand test: 1. Soil P levels in a field vary depending on location, past management, and time of year. Examples of variables include placement of P fertilizer (broadcast or banded; in rows or between rows), soil texture, organic matter content, and application of manure or other fertilizer. Using a soil probe, gather at least 1 small samples to a depth of 8 inches or less randomly from an area that represents a particular soil type and management history. Place samples in the small plastic container and mix. Samples gathered for no-till cropping, forage establishment, and environmental purposes can be taken to a shallower depth. Do not include large stones and plant residue. Repeat this step for each sampling area. 2. Neutralize hands by rubbing moist soil across palms. Discard soil. Place a scoop of the mixed soil in palm of hand and saturate with clean water (distilled water or rainwater). 3. Squeeze hand gently until a soil and water slurry forms. 4. Touch tip of phosphate test strip to the soil and water slurry. Leave until the liquid is drawn up at least 1/8 to 3/16 inch beyond the area covered by the soil (fig. 4). 5. After 1 to 2 minutes, compare color of wet test strip to color chart on the test strip container (fig. 5). The color on the chart that most closely matches the color on the test strip indicates the amount of phosphate in the saturated soil. Record value in table 1. Figure 4. Quick in-field hand test. Page 4 Guides for Educators (May 214)

29 Soil Health Phosphorus USDA-NRCS Figure 5. Phosphate color chart. 1:1 soil to water phosphate test for classroom: 1. Soil sampling should be completed as instructed in step 1 under Quick in-field hand test. 2. Fill scoop (29.5 ml) with the mixed soil, tamping down during filling by carefully striking the scoop on a hard, level surface. Put soil in vial. Add one scoopful (29.5 ml) of water to the vial, resulting in a 1:1 ratio of soil to water, on a volume basis. 3. Tightly cap the vial and shake 25 times. Let settle for 1 minute. Remove cap, and carefully decant 1/16 inch of soil and water slurry into cap. 4. Allow to settle for 2 to 3 minutes. Touch end of phosphate test strip to soil and water slurry. Leave until the liquid is drawn up at least 1/8 to 3/16 inch beyond the area covered by the soil (fig. 6). 5. After 1 to 2 minutes, compare color of wet test strip to color chart on test strip container (fig. 5). The color on the chart that most closely matches the color on the test strip indicates the index value of phosphate in the water-saturated soil. Record value in table 1. Figure 6. 1:1 soil to water test. Compare water-soluble phosphate (PO 4 ) test results to other P test method results, PO 4 categories, and recommended fertilizer rates in table 1. Answer discussion questions. Interpretations Recommendations for fertilizer and PO 4 categories will vary with the type of crop grown and Land Grant University recommendations. Page 5 Guides for Educators (May 214)

30 Soil Health Phosphorus USDA-NRCS Table 1. Phosphorus test results and agronomic recommendations for corn grown in Nebraska* Site (Based on standard P tests and water-soluble PO 4 test for a 1:1 soil to water mixture.) Water-soluble PO 4 in 1:1 soil to water mixture PO 4 (ppm) Relative PO 4 level Soil P relational values by P test method (ppm) Watersoluble PO 4 *** Olsen P**** Bray 1-P**** Relative PO 4 level**** Recommended fertilizer for corn (lbs P 2 O 5 /acre and [P/ac**]) Broadcast**** Band**** Ex.1 16 High Very low 8 [35] 4 [17] Low 4 [17] 2 [9] Medium [9] High >2 >2 >3 Very high *If animal manure or compost has been applied, most soils generally have a medium to very high level of phosphorus and do not need supplemental fertilization. Land Grant University recommendations should be followed. Further guidance is provided in the NRCS Nutrient Management Standard 59 ( **Recommendations are based on use of synthetic P fertilizer, but they can also be used for organic sources of P such as rock phosphate or soft phosphate that can supply equivalent levels of available P over time. ***Water-soluble P (PO 4 ) test (Hach trademark) for 1:1 soil to water mixture based on comparison with Bray 1-P and Olsen P tests for nineteen benchmark soils (Bray 1-P test for soils with ph <7.2; Olsen P test for soils with ph >7.2). Water-soluble Aquachek-based P recommendations agreed for twelve soils (63 percent) and were borderline for another three soils, for a total of 79 percent. Four 1:1 soil to water mixture/water-soluble PO 4 tests indicated higher available P than results of standard Bray 1-P and Olsen P tests. ****Based on Fertilizer Suggestions for Corn, University of Nebraska NebGuide G A, revised September, 21. For soils that have a medium level of phosphorus, applying 1 to 2 pounds per acre of P 2 O 5 may increase early growth and application is optional. Page 6 Guides for Educators (May 214)

31 Soil Health Phosphorus USDA-NRCS Are soil phosphate levels adequate? What are the relative P levels and recommended rate of application of P 2 O 5 fertilizer according to table 1? Do current management practices limit phosphorus losses from erosion and sedimentation? Do they prevent soluble P in runoff or drainage tiles from reaching streams or lakes? Are proper management practices being used to maintain soil health (compaction, ph, salinity, and organic matter content)? Do they properly manage the placement and application rate of P fertilizer or manure? Why or why not? Immobilization. Temporary tying up of water-soluble P as a result of soil micro-organisms decomposing plant residue. Immobilized P will eventually become available for plant use as decomposition progresses. Mineralization. Conversion of nutrients in soil organic matter (e.g., phosphorus, nitrogen, and sulfur) to inorganic forms that are available for crop use; occurs during respiration. Orthophosphate. Form of phosphorus absorbed by plants, generally H 2 PO 4 - or HPO Glossary Phosphorus cycle. Circulation of many different forms of P in soil. Some forms are available for plant use, and some are not, such as those fixed to iron, aluminum, and calcium minerals (fig. 1). Phosphorus fixation. Phosphate that is bound to iron, aluminum, and calcium minerals and sorbed on clay minerals. Fixation and availability of P vary with soil ph (fig. 2). Soil phosphate. Form of P that is available for plant use, expressed as PO 4. USDA is an equal opportunity provider and employer. Page 7 Guides for Educators (May 214)

32 Soil Quality Information Sheet Soil Quality Concerns: Pesticides USDA Natural Resources Conservation Service January 1998 What are pesticides? Pesticides are synthetic organic chemicals used to control weeds in fields and lawns, and unwanted or harmful pests, such as insects and mites that feed on crops. Pesticides are divided into categories according to the target organisms they are designed to control (e.g., insecticides control insects). Herbicides are by far the most commonly used pesticides in the United States. They range from non selective to highly selective for control of specific weeds in specific crops, with different products having postemergence, preplant, and preemergence uses. Insecticides are second in usage, and fungicides are third. human and animal health, and beneficial plants and soil organisms. Pesticides can move off-site contaminating surface and groundwater and possibly causing adverse impacts on aquatic ecosystems. What are pesticide formulations? The formulation is the chemical and physical form in which the pesticide is sold for use. The active ingredient (a.i.) is the chemical in the formulation that has the specific effect on the target organism. The formulation improves the properties of the pesticides for storage, handling, application, effectiveness, or safety. Examples of formulated products are wettable powders and waterdispersible granules. A single pesticide is often sold in several different formulations, depending on use requirements and application needs. Pesticide mode of action Mode of action refers to the mechanism by which the pesticide kills or interacts with the target organism. Effects of Pesticides on Soil Quality The capacity of the soil to filter, buffer, degrade, immobilize, and detoxify pesticides is a function or quality of the soil. Soil quality also encompasses the impacts that soil use and management can have on water and air quality, and on human and animal health. The presence and bio-availability of pesticides in soil can adversely impact Contact pesticides kill the target organism by weakening or disrupting the cellular membranes; death can be very rapid. Systemic pesticides must be absorbed or ingested by the target organism to disrupt its physiological or metabolic processes; generally they are slow acting. How effective the pesticides are at killing the target organisms (efficacy) depends on the properties of the pesticide and the soil, formulation, application technique, agricultural management, characteristics of the crop, environmental or weather conditions, and the nature and behavior of the target organism.

33 Fate of pesticides in the environment Ideally, a pesticide stays in the treated area long enough to produce the desired effect and then degrades into harmless materials. Three primary modes of degradation occur in soils: biological - breakdown by micro-organisms chemical - breakdown by chemical reactions, such as hydrolysis and redox reactions photochemical - breakdown by ultraviolet or visible light The rate at which a chemical degrades is expressed as the half-life. The half-life is the amount of time it takes for half of the pesticide to be converted into something else, or its concentration is half of its initial level. The half-life of a pesticide depends on soil type, its formulation, and environmental conditions (e.g., temperature, moisture). Other processes that influence the fate of the chemical include plant uptake, soil sorption, leaching, and volatilization. If pesticides move off-site (e.g., wind drift, runoff, leaching), they are considered to be pollutants. The potential for pesticides to move off-site depends on the chemical properties and formulation of the pesticide, soil properties, rate and method of application, pesticide persistence, frequency and timing of rainfall or irrigation, and depth to ground water. Pesticide toxicity The toxicity level of a pesticide depends on the deadliness of the chemical, the dose, the length of exposure, and the route of entry or absorption by the body. Pesticide degradation in soil generally results in a reduction in toxicity; however, some pesticides have breakdown products (metabolites) that are more toxic than the parent compound. Pesticides are classified according to their potential toxicity to humans and other animals and organisms, as restricted-use (can only be purchased and applied by certified persons who have had training in pesticide application), and general use (may be purchased and applied by any person). Retention of pesticides in the soil Retention refers to the ability of the soil to hold a pesticide in place and not allow it to be transported. Adsorption is the primary process of how the soil retains a pesticide and is defined as the accumulation of a pesticide on the soil particle surfaces. Pesticide adsorption to soil depends on both the chemical properties of the pesticide (i.e., water solubility, polarity) and properties of the soil (i.e., organic matter and clay contents, ph, surface charge characteristics, permeability). For most pesticides, organic matter is the most important soil property controlling the degree of adsorption. For most pesticides, the degree of adsorption is described by an adsorption distribution coefficient (K d ), which is mathematically defined as the amount of pesticide in soil solution divided by the amount adsorbed to the soil. (Prepared by the National Soil Survey Center in cooperation with the Soil Quality Institute, NRCS, USDA, and the National Soil Tilth Laboratory, Agricultural Research Service, USDA). Use and application considerations Apply pesticides at the lowest effective level. Avoid unnecessary pesticide treatments. Use Integrated Pest Management. Follow all label instructions. Apply proper rates and times as label indicates. Calibrate application equipment. Apply formulations that minimize drift. Use safety equipment when handling. Store and dispose of pesticide containers properly. Use biological controls when appropriate. Alter farming or cropping systems to control pests. Use disease and insect resistant crop varieties. Visit our Web site: The U. S. Department of Agriculture (USDA) prohibits discrimination in its programs on the basis of race, color, national origin, gender, religion, age, disability, political beliefs, sexual orientation, and marital or family status. (Not all prohibited bases apply to all programs.) Persons with disabilities who require alternative means for communication of program information (Braille, large print, audiotape, etc.) should contact USDA s TARGET Center at (22) (voice and TDD). To file a complaint of discrimination, write USDA, Director, Office of Civil Rights, Room 326W, Whitten Building, 14th and Independence Avenue, SW, Washington, DC or call (22) (voice or TDD). USDA is an equal opportunityprovider and employer.

34 Soil Quality Agronomy Technical Note No. 4 Effect of Soil Quality on Nutrient Efficiency United States Department of Agriculture Natural Resources Conservation Service Soil Quality Institute 215 Pammel Dr. Ames, IA Technical Note No. 4 August, 1997 This is the fourth Agronomy fact sheet in a series on on soil quality. This fact sheet is general. For specific application, contact your NRCS State Agronomist. Page 1 Nutrient efficiency is a measure of how much crop is produced per unit of nutrient supplied. The higher the efficiency, the more product is produced per unit of nutrient. The quality of soil affects nutrient use efficiency. Soil quality is measured or evaluated by a number of indicators. This technical note will discuss how 13 indicators relates to nutrient efficiency. 1. Soil Quality definition with regards to nutrients A healthy soil functioning at nearly full capacity stores and cycles nutrients and allows crops to grow and use nutrients efficiently. In a healthy soil, nutrients become available when the plants need them. There is little risk for crop nutrients to move below the root zone through leaching, off the edge of field by runoff and erosion, or above the crop canopy by volatilization. Crop nutrients that move beyond the crop s zone of uptake could potentially contaminate the environment. 2. Erosion Erosion and runoff are both detrimental to nutrient management. Nutrients contained in the topsoil, along with soil organic matter, can be carried away by erosion or washed out with runoff water. The organic matter is the first to be transported by water or wind because of its lower specific gravity. Additional nutrients are required to maintain productivity lost when topsoil is carried away by erosion. 3. Deposition of Sediment Sediment additions in the field can be good or bad. Some sediment, especially the finer clay particles and organic matter, bring in nutrients. The coarser sediments, like sands, do not have a high nutrient content and tend to cover the topsoil that is in place. Coarser textured soils also lack moisture-holding and pesticide-retention capacity. 4. Compaction Compact soils restrict the movement of roots. Less root volume in the soil prevents nutrient uptake. Compaction also restricts the diffusion and flow of nutrients in the soil. Few roots and limited nutrient movement can result in stunted growth because the plant is unable to take up the nutrients in the soil. Compacted soils retard air movement and gas exchange in the root zone. This can lead to nutrient losses, like denitrification or toxic gas build-up near the roots. 5. Soil Aggregation at the Soil Surface Good soil aggregation means better water and nutrient movement through the soil. More aggregation means more of the surface area of the soil particles have capacity for adsorbed nutrients. Surface aggregation allows pore space for water infiltration and gas exchanges. Good soil aggregation is closely tied to the amount of active organic matter and to biological activity. Thus soil aggregation is connected to nutrient cycling. 6. Infiltration Plants require water. Nutrients move with the water through the soil pores and are absorbed into the plant. When nutrients are applied to the soil surface, as in no-till systems, water is required to move the nutrients down into the root zone. Good soil infiltration permits this to happen. Nutrients that are not carried

35 into the root zone are susceptible to runoff. Percolating water carries the nutrients deeper into the root zone and also removes harmful salts that may accumulate there. 7. Soil Crusting Crusting seals the soil surface and restricts water infiltration and gas exchange. If not allowed to infiltrate, surface applied nutrients on crusted soils are susceptible to runoff and wind transport. Crusting also reduces seed germination and seedling survival which directly has an effect on the plant population and the amount of nutrients necessary for the crop. 11. Biological Activity A healthy soil has a diverse set of macro and micro organisms that assure a well functioning soil food web. Microorganisms decompose organic material, store nutrients in their bodies, and as they decay or become food for other organisms, they release nutrients. Some small animals like insects and crustacea carry organic material and related nutrients into the soil and aid in its decomposition. Some microorganisms have a symbiotic relationship with plants such as mycorrhiza. Mycorrhiza live in plant roots and help the plants assimilate water and nutrients. United States Department of Agriculture Natural Resources Conservation Service Soil Quality Institute 215 Pammel Dr. Ames, IA Technical Note No. 4 August, 1997 Page 2 8. Nutrient Loss or Imbalance Nutrients need to be applied according to the crop and soil requirements. Soil and plant analyses are a good way to determine the amount of nutrients needed. Over-application of nutrients can lead to plant toxicity, poor ph reaction, and excess nutrients susceptible to runoff, leaching, and volatilization. A deficiency in nutrients will not sustain optimum plant growth. 9. Pesticide Carryover Pesticides with residual soil activity can stunt growth of subsequent crops. If roots are affected, their ability to absorb nutrients will be lessened. Any effect on plant photosynthesis will reduce nutrient uptake and metabolism. Without pesticide or weed control, weeds can utilize nutrients in competition of the crop. The weed residue may not decompose and recycle plant nutrients for the subsequent crops. 1. Organic Matter Soil organic matter is a very valuable component of the topsoil. Organic matter stores nutrients, feeds soil organisms that decompose organic material, and return the basic nutrients to the soil. Organic matter holds soil moisture for plant use. Soil organic matter is developed by combining of carbon, oxygen, and nitrogen plus other nutrients in the soil. Nitrogen and other nutrients must be available to soil microorganisms for development of organic matter. 12. Weeds and Pathogens Nutrients can be used by crops or by weeds. Weeds utilize nutrients, but fail to produce a marketable commodity. So, the nutrients are not efficiently used to grow crops. The same is true for crops that are attacked by disease and insects. Efficient utilization means nutrients are converted to a harvestable product. 13. Extreme Soil Moisture Conditions The amount of soil moisture impacts nutrient cycling. A dry soil does not promote root extension in the root zone. And, since nutrients are carried by water, plants are unable to obtain adequate nutrition. Waterlogged soils affect the transformation of nutrients. Phosphorus becomes more mobile and less attached to minerals in waterlogged conditions. Nitrate nitrogen is denitrified by changing form from a liquid to a gas which can be lost to the atmosphere. Roots consume oxygen and respire carbon dioxide. Because gases are transported much more slowly through water (about one ten thousanth slower) than air, some gases such as carbon dioxide can accumulate in the soil and be toxic to roots. The United States Department of Agriculture (USDA) prohibits discrimination in its programs on the basis of race, color, national origin, sex, religion, age, disability, political beliefs and marital or familial status. (Not all prohibited bases apply to all programs.) Persons with disabilities who require alternative means for communication of program information (Braille, large print, audiotape, etc.) should contact the USDA s TARGET Center at (22) (voice and TDD). To file a complaint, write the Secretary of Agriculture, U.S. Department of Agriculture, Washington, D.C., 225, or call (voice) or (22) (TDD). USDA is an equal opportunity employer.

36 USDA Natural Resources Conservation Service Indicator B Test L Function D/N Soil Enzymes Soil Quality Indicators Soil enzymes increase the reaction rate at which plant residues decompose and release plant available nutrients. The substance acted upon by a soil enzyme is called the substrate. For example, glucosidase (soil enzyme) cleaves glucose from glucoside (substrate), a compound common in plants. Enzymes are specific to a substrate and have active sites that bind with the substrate to form a temporary complex. The enzymatic reaction releases a product, which can be a nutrient contained in the substrate. Sources of soil enzymes include living and dead microbes, plant roots and residues, and soil animals. Enzymes stabilized in the soil matrix accumulate or form complexes with organic matter (humus), clay, and humus-clay complexes, but are no longer associated with viable cells. It is thought that 4 to 6% of enzyme activity can come from stabilized enzymes, so activity does not necessarily correlate highly with microbial biomass or respiration. Therefore, enzyme activity is the cumulative effect of long term microbial activity and activity of the viable population at sampling. However, an example of an enzyme that only reflects activity of viable cells is dehydrogenase, which in theory can only occur in viable cells and not in stabilized soil complexes. Factors Affecting Inherent - Soil enzymes have varying optimum ph and temperature values at which they function most effectively. For example, the activity of phosphatase, aryl sulfatase, and amidase involved in phosphorus, sulfur, and nitrogen cycling, respectively, is strongly correlated to variations in soil ph. Since enzyme structure and substrate binding can be altered by heat and extreme cold temperature, enzyme activity decreases above and below the optimum temperature. The activity of many enzymes often correlates with soil moisture content, as well. Drought may suppress enzyme activity. Soil texture influences enzyme activity, and normally enzyme activities are significantly and positively correlated with clay content. Clayey soils have greater ability to store organic matter that promotes microbial communities, and clay forms clay-enzyme complexes. In contrast, sandy soils Helping People Help the Land... tend to exhibit low rates of enzyme activity because they are naturally low in organic matter and have poor water holding capacity which results in lower microbial biomass and therefore lower enzyme activity. Dynamic - Addition of organic amendments and adoption of management practices that increase soil organic matter lead to increased enzyme activity (figs 1 and 2). Plant roots stimulate enzyme activity because of their positive effect on microbial activity and production of exudates rich in substrates acted on by enzymes. Elevated soil concentrations of chemical compounds that are end products of enzymatic reactions can inhibit enzyme activity by feedback inhibition. For example, phosphatase activity increases in phosphorus deficient soil, but its activity decreases in soil with high phosphorus concentration. Similarly, urease activity may be suppressed by ammonia-based nitrogen fertilizer because ammonium is the product of urease activity (fig 2). Compaction may limit the activity of enzymes involved in nutrient mineralization because of decreased oxygen in the soil for those reactions or organisms requiring an aerobic environment. Conversely, anaerobic conditions from compaction or water saturation increase enzymatic reaction rates related to denitrification. Application of materials containing heavy metals can reduce enzyme activity (e.g., amidase) due to their toxic effect on soil organisms and roots or direct inhibition of enzyme reactions. ß-glucosidase Activity Grass (burned) Grass (not burned) Vegetable Rotation Fescue-clover Figure 1. Effects of cropping systems on ß-glucosidase (adapted from Dick 1994).

37 Relationship to Soil Function Enzymes respond to soil management changes long before other soil quality indicator changes are detectable. Soil enzymes play an important role in organic matter decomposition and nutrient cycling (table 1). Some enzymes only facilitate the breakdown of organic matter (e.g., hydrolase, glucosidase), while others are involved in nutrient mineralization (e.g., amidase, urease, phosphatase, sulfates). With the exception of phosphatase activity, there is no strong evidence that directly relates enzyme activity to nutrient availability or crop production. The relationship may be indirect considering nutrient mineralization to plant available forms is accomplished with the contribution of enzyme activity. Problems with Poor Activity Absence or suppression of soil enzymes prevents or reduces processes that can affect plant nutrition. Poor enzyme activity (e.g., pesticide degrading enzymes) can result in an accumulation of chemicals that are harmful to the environment; some of these chemicals may further inhibit soil enzyme activity. Improving Enzyme Activity Organic amendment applications, crop rotation, and cover crops have been shown to enhance enzyme activity (figs 1 and 2). The positive effect of pasture (fig 2) is associated with the input of animal manure and less soil disturbance. Agricultural methods that modify soil ph (e.g., liming) can also change enzyme activity. Measuring Enzyme Activity Enzymes are measured indirectly by determining their activity in the laboratory using biochemical assays. Enzyme assays reflect potential activity and do not represent true in situ activity levels and must be viewed as an index. Interpretation and Assessment When possible, compare the site of interest to samples taken from an adjacent, undisturbed site on the same soil type. Alternatively, for a newly implemented land management system, track changes from time zero to five or more years with annual sampling to detect temporal changes in activity of soil enzymes. Specialized equipment, shortcuts, tips: A spectrophotometer, and in some cases a fume hood, centrifuge, and/or shaker. For better results, use the enzyme optimum temperature and ph. Time needed: variable, 3 to 6 minutes References: Bandick AK and Dick RP Field management effects on enzyme activities. Soil Biology and Biochemistry 31: Dick RP Soil Enzyme Activity as an Indicator of Soil Quality. In: Doran JW et al., editors. Defining soil quality for a sustainable environment.. Madison, WI. p Tabatabai MA Soil Enzymes. In: Weaver RW et al., editors. Methods of soil analysis. Part 2. Microbiological and Biochemical Properties. p Urease Activity No Nitrogen 8 lbs N/A Peas Manure Pasture Figure 2. Effects of management on urease activity (adapted from Bandick and Dick 1999). Table 1. Role of soil enzymes Enzyme Organic Matter Substances Acted On End Product Significance Predictor of Soil Function Beta glucosidase carbon compounds glucose (sugar) energy for microorganisms organic matter decomposition FDA hydrolysis organic matter carbon and various nutrients energy and nutrients for microorganisms, measure microbial biomass organic matter decomposition nutrient cycling Amidase carbon and nitrogen compounds ammonium (NH 4 ) plant available NH 4 nutrient cycling Urease nitrogen (urea) ammonia (NH 3 ) and carbon dioxide (CO 2 ) plant available NH 4 nutrient cycling Phosphatase phosphorus phosphate (PO 4 ) plant available P nutrient cycling Sulfatase sulfur sulfate (SO 4 ) plant available S nutrient cycling USDA is an equal opportunity provider and employer. October 21

38 SOIL QUALITY URBAN TECHNICAL NOTE No. 3 Heavy Metal Soil Contamination Introduction United States Department of Agriculture Natural Resources Conservation Service Soil Quality Institute 411 S. Donahue Dr. Auburn, AL X-177 Urban Technical Note No. 3 September, 2 This is the third note in a series of Soil Quality- Urban technical notes on the effects of land management on soil quality. Soil is a crucial component of rural and urban environments, and in both places land management is the key to soil quality. This series of technical notes examines the urban activities that cause soil degradation, and the management practices that protect the functions urban societies demand from soil. This technical note focuses on heavy metal soil contamination. Metals in Soil Mining, manufacturing, and the use of synthetic products (e.g. pesticides, paints, batteries, industrial waste, and land application of industrial or domestic sludge) can result in heavy metal contamination of urban and agricultural soils. Heavy metals also occur naturally, but rarely at toxic levels. Potentially contaminated soils may occur at old landfill sites (particularly those that accepted industrial wastes), old orchards that used insecticides containing arsenic as an active ingredient, fields that had past applications of waste water or municipal sludge, areas in or around mining waste piles and tailings, industrial areas where chemicals may have been dumped on the ground, or in areas downwind from industrial sites. Excess heavy metal accumulation in soils is toxic to humans and other animals. Exposure to heavy metals is normally chronic (exposure over a longer period of time), due to food chain transfer. Acute (immediate) poisoning from heavy metals is rare through ingestion or dermal contact, but is possible. Chronic problems associated with long-term heavy metal exposures are:! Lead mental lapse.! Cadmium affects kidney, liver, and GI tract.! Arsenic skin poisoning, affects kidneys and central nervous system. The most common problem causing cationic metals (metallic elements whose forms in soil are positively charged cations e.g., Pb 2+ ) are mercury, cadmium, lead, nickel, copper, zinc, chromium, and manganese. The most common anionic compounds (elements whose forms in soil are combined with oxygen and are negatively charged e.g., MoO 4 2- ) are arsenic, molybdenum, selenium, and boron. 1

39 Prevention of Heavy Metal Contamination Preventing heavy metal pollution is critical because cleaning contaminated soils is extremely expensive and difficult. Applicators of industrial waste or sludge must abide by the regulatory limits set by the U.S. Environmental Protection Agency (EPA) in Table 1. Table 1. Regulatory limits on heavy metals applied to soils (Adapted from U.S. EPA, 1993). Heavy metal Maximum concentration in sludge (mg/kg or Annual pollutant loading rates Cumulative pollutant loading rates ppm) (kg/ha/yr) (lb/a/yr) (kg/ha) (lb/a) Arsenic Cadmium Chromium ,679 Copper ,34 Lead Mercury Molybdenum Nickel Selenium Zinc Prevention is the best method to protect the environment from contamination by heavy metals. With the above table, a simple equation is used to show the maximum amount of sludge that can be applied. For example, suppose city officials want to apply the maximum amount of sludge (kg/ha) on some agricultural land. The annual pollutant-loading rate for zinc is 14 kg/ha/yr (from Table 1). The lab analysis of the sludge shows a zinc concentration of 75 mg/kg (mg/kg is the same as parts per million). How much can the applicator apply (tons/a) without exceeding the 14 kg/ha/yr? Solution: (1) Convert mg to kg (1,, mg = 1kg) so all units are the same: 75 mg X (1 kg/1,, mg) =.75 kg (2) Divide the amount of zinc that can be applied by the concentration of zinc in the sludge: (14 kg Zn/ha) / (.75 kg Zn/kg sludge) =18,667 kg sludge/ha (3) Convert to lb/a: 18,667 kg/ha X.893 = 16,669 lbs/a Convert lbs to tons: 16,669 lb/a / 2, lb/t = 8.3 T sludge per acre 2

40 Traditional Remediation of Contaminated Soil Once metals are introduced and contaminate the environment, they will remain. Metals do not degrade like carbon-based (organic) molecules. The only exceptions are mercury and selenium, which can be transformed and volatilized by microorganisms. However, in general it is very difficult to eliminate metals from the environment. Traditional treatments for metal contamination in soils are expensive and cost prohibitive when large areas of soil are contaminated. Treatments can be done in situ (on-site), or ex situ (removed and treated off-site). Both are extremely expensive. Some treatments that are available include: 1. High temperature treatments (produce a vitrified, granular, non-leachable material). 2. Solidifying agents (produce cement-like material). 3. Washing process (leaches out contaminants). Management of Contaminated Soil Soil and crop management methods can help prevent uptake of pollutants by plants, leaving them in the soil. The soil becomes the sink, breaking the soil-plantanimal or human cycle through which the toxin exerts its toxic effects (Brady and Weil, 1999). The following management practices will not remove the heavy metal contaminants, but will help to immobilize them in the soil and reduce the potential for adverse effects from the metals Note that the kind of metal (cation or anion) must be considered: 1. Increasing the soil ph to 6.5 or higher. Cationic metals are more soluble at lower ph levels, so increasing the ph makes them less available to plants and therefore less likely to be incorporated in their tissues and ingested by humans. Raising ph has the opposite effect on anionic elements. 2. Draining wet soils. Drainage improves soil aeration and will allow metals to oxidize, making them less soluble. Therefore when aerated, these metals are less available. The opposite is true for chromium, which is more available in oxidized forms. Active organic matter is effective in reducing the availability of chromium. 3. Applying phosphate. Heavy phosphate applications reduce the availability of cationic metals, but have the opposite effect on anionic compounds like arsenic. Care should be taken with phosphorus applications because high levels of phosphorus in the soil can result in water pollution. 3

41 4. Carefully selecting plants for use on metal-contaminated soils Plants translocate larger quantities of metals to their leaves than to their fruits or seeds. The greatest risk of food chain contamination is in leafy vegetables like lettuce or spinach. Another hazard is forage eaten by livestock. Plants for Environmental Cleanup Research has demonstrated that plants are effective in cleaning up contaminated soil (Wenzel et al., 1999). Phytoremediation is a general term for using plants to remove, degrade, or contain soil pollutants such as heavy metals, pesticides, solvents, crude oil, polyaromatic hydrocarbons, and landfill leacheates For example, prairie grasses can stimulate breakdown of petroleum products. Wildflowers were recently used to degrade hydrocarbons from an oil spill in Kuwait. Hybrid poplars can remove ammunition compounds such as TNT as well as high nitrates and pesticides (Brady and Weil, 1999). Plants for Treating Metal Contaminated Soils Plants have been used to stabilize or remove metals from soil and water. The three mechanisms used are phytoextraction, rhizofiltration, and phytostabilization. This technical note will define rhizofiltration and phytostabilization but will focus on phytoextraction. Rhizofiltration is the adsorption onto plant roots or absorption into plant roots of contaminants that are in solution surrounding the root zone (rhizosphere). Rhizofiltration is used to decontaminate groundwater. Plants are grown in greenhouses in water instead of soil. Contaminated water from the site is used to acclimate the plants to the environment. The plants are then planted on the site of contaminated ground water where the roots take up the water and contaminants. Once the roots are saturated with the contaminant, the plants are harvested including the roots. In Chernobyl, Ukraine, sunflowers were used in this way to remove radioactive contaminants from groundwater (EPA, 1998). Phytostabilization is the use of perennial, non-harvested plants to stabilize or immobilize contaminants in the soil and groundwater. Metals are absorbed and accumulated by roots, adsorbed onto roots, or precipitated within the rhizosphere. Metal-tolerant plants can be used to restore vegetation where natural vegetation is lacking, thus reducing the risk of water and wind erosion and leaching. Phytostabilization reduces the mobility of the contaminant and prevents further movement of the contaminant into groundwater or the air and reduces the bioavailability for entry into the food chain. Phytoextraction Phytoextraction is the process of growing plants in metal contaminated soil. Plant roots then translocate the metals into aboveground portions of the plant. After plants have grown for some time, they are harvested and incinerated or composted to recycle the metals. Several crop growth cycles may be needed to decrease 4

42 contaminant levels to allowable limits. If the plants are incinerated, the ash must be disposed of in a hazardous waste landfill, but the volume of the ash is much smaller than the volume of contaminated soil if dug out and removed for treatment. (See box.) Example of Disposal Excavating and landfilling a 1-acre contaminated site to a depth of 1 foot requires handling roughly 2, tons of soil. Phytoextraction of the same site would result in the need to handle about 5 tons of biomass, which is about 1/4 of the mass of the contaminated soil. In this example, if we assume the soil was contaminated with a lead concentration of 4 ppm, six to eight crops would be needed, growing four crops per season (Phytotech, 2). Phytoextraction is done with plants called hyperaccumulators, which absorb unusually large amounts of metals in comparison to other plants. Hyperaccumulators contain more than 1, milligrams per kilogram of cobalt, copper, chromium, lead, or nickel; or 1, milligrams per kilogram (1 %) of manganese or zinc in dry matter (Baker and Brooks, 1989). One or more of these plant types are planted at a particular site based on the kinds of metals present and site conditions. Tables 2 and 3 demonstrate the importance of using hyperaccumulators. Table 2. Percentage decrease in water-extractable zinc and cadmium in three soils after growth of Alpine pennycress (Thlaspi caerulescens) (McGrath, 1998). Site Sampled Zn Cd Farm 28 1 Garden Mountain 64 7 Table 3. Removal of zinc in a hypothetical 4.5 T/A (dry matter) crop growing in soil contaminated with 1 (ppm) zinc with a target of 5 ppm, showing the importance of hyperaccumulation (>1, ppm zinc) (McGrath, 1998). ppm Zn Lbs. of Zn % of soil total years to target in plant removed in one crop , , , Phytoextraction is easiest with metals such as nickel, zinc, and copper because these metals are preferred by a majority of the 4 hyperaccumlator plants. Several plants in the genus Thlaspi (pennycress) have been known to take up more than 3, ppm (3%)of zinc in their tissues. These plants can be used as ore because of the high metal concentration (Brady and Weil, 1999). 5

43 Of all the metals, lead is the most common soil contaminant (EPA, 1993). Unfortunately, plants do not accumulate lead under natural conditions. A chelator such as EDTA (ethylenediaminetetraacetic acid) has to be added to the soil as an amendment. The EDTA makes the lead available to the plant. The most common plant used for lead extraction is Indian mustard (Brassisa juncea). Phytotech (a private research company) has reported that they have cleaned up leadcontaminated sites in New Jersey to below the industrial standards in 1 to 2 summers using Indian mustard (Wantanabe, 1997). Plants are available to remove zinc, cadmium, lead, selenium, and nickel from soils at rates that are medium to long-term, but rapid enough to be useful. Many of the plants that hyperaccumulate metals produce low biomass, and need to be bred for much higher biomass production. Current genetic engineering efforts at USDA in Beltsville, MD, are aimed toward developing pennycress (Thlaspi) that is extremely zinc tolerant. These taller-thannormal plants would have more biomass, thereby taking up larger quantities of contaminating metals (Watanabe, 1997). Traditional cleanup in situ may cost between $1. and $1. per cubic meter (m 3 ), whereas removal of contaminated material (ex situ) may cost as high $3. to $3/ m 3. In comparison, phytoremediation may only cost $.5/ m 3 (Watanabe, 1997). Future Prospects Phytoremediation has been studied extensively in research and small-scale demonstrations, but in only a few full-scale applications. Phytoremediation is moving into the realm of commercialization (Watanabe, 1997). It is predicted that the phytoremediation market will reach $214 to $37 million by the year 25 (Environmental Science & Technology, 1998). Given the current effectiveness, phytoremediation is best suited for cleanup over a wide area in which contaminants are present at low to medium concentrations. Before phytoremediation is fully commercialized, further research is needed to assure that tissues of plants used for phytoremediation do not have adverse environmental effects if eaten by wildlife or used by humans for things such as mulch or firewood (EPA, 1998). Research is also needed to find more efficient bioaccumulators, hyperaccumulators that produce more biomass, and to further monitor current field trials to ensure a thorough understanding. There is the need for a commercialized smelting method to extract the metals from plant biomass so they can be recycled. Phytoremediation is slower than traditional methods of removing heavy metals from soil but much less costly. Prevention of soil contamination is far less expensive than any kind of remediation and much better for the environment. 6

44 References Baker, A.J.M., and R.R. Brooks Terrestrial plants which hyperaccumulate metallic elements a review of their distribution, ecology, and phytochemistry. Biorecovery 1:81:126. Brady, N.C., and R.R. Weil The nature and properties of soils. 12th ed. Prentice Hall. Upper Saddle River, NJ. Environmental Science & Technology Phytoremediation; forecasting. Environmental Science & Technology. Vol. 32, issue 17, p.399a. McGrath, S.P Phytoextraction for soil remediation. p In R. Brooks (ed.) Plants that hyperaccumulate heavy metals their role in phytoremediation, microbiology, archaeology, mineral exploration and phytomining. CAB International, New York, NY. Phytotech. 2. Phytoremediation technology. U.S. EPA Clean Water Act, sec. 53, vol. 58, no. 32. (U.S. Environmental Protection Agency Washington, D.C.). U.S. EPA A citizen s guide to phytoremediation. Watanabe, M.E Phytoremediation on the brink of commercialization. Environmental Science & Technology/News. 31: Wenzel, W.W., Adriano, D.C., Salt, D., and Smith, R Phytoremediation: A plant-microbe based remediation system. p In D.C. Adriano et al. (ed.) Bioremediation of contaminated soils. American Society of Agronomy, Madison, WI. Disclaimer Trade names are used solely to provide specific information. Mention of a trade name does not constitute a guarantee of the product by the U.S. Department of Agriculture nor does it imply endorsement by the Department or the Natural Resources Conservation Service over comparable products that are not named. The U. S. Department of Agriculture (USDA) prohibits discrimination in all its programs and activities on the basis of race, color, national origin, sex, religion, age, disability, political beliefs, sexual orientation, or marital or family status. (Not all prohibited bases apply to all programs.) Persons with disabilities who require alternative means for communications of program information (Braille, large print, audiotape, etc.) should contact USDA s TARGET Center at (22) (voice and TDD). To file a complaint of discrimination, write USDA, Director, Office of Civil Rights, Room 326W, Whitten Building, 14th and Independence Avenue, SW, Washington, DC or call (22) (voice and TDD). USDA is an equal opportunity provider and employer. 7

45 Animal Manures for Increasing Organic Matter and Supplying Nutrients The quickest way to rebuild a poor soil is to practice dairy farming, growing forage crops, buying...grain rich in protein, handling the manure properly, and returning it to the soil promptly. J. L. HILLS, C. H. JONES, AND C. CUTLER, 198 Once cheap fertilizers became widely available after World War II, many farmers, extension agents, and scientists looked down their noses at manure. People thought more about how to get rid of manure than how to put it to good use. In fact, some scientists tried to find out the absolute maximum amount of manure that could be applied to an acre without reducing crop yields. Some farmers who didn t want to spread manure actually piled it next to a stream and hoped that next spring s flood waters would wash it away. We now know that manure, like money, is better spread around than concentrated in a few places. The economic contribution of farm manures can be considerable. On a national basis, the manure from 1 million cattle, 6 million hogs, and 9 billion chickens contains about 23 million tons of nitrogen. At a value of 5 cents per pound, that works out to a value of about $25 billion for just the N contained in animal manures. The value of the nutrients in manure from a 1-cow dairy farm may exceed $2, per year; manure from a 1-sow farrow-to-finish operation is worth about $16,; and manure from a 2,bird broiler operation is worth about $6,. The other benefits to soil organic matter buildup, such as enhanced soil structure and better diversity and activity of soil organisms, may double the value of the manure. If you re not getting the full fertility benefit from manures on your farm, you may be wasting money. Animal manures can have very different properties, depending on the animal species, feed, bedding, handling, and manure-storage practices. The amounts of nutrients in the manure that become available to crops also depend on what time of year the manure is applied and how quickly it is worked into the soil. In addition, the influence of manure on soil organic matter and plant growth is influenced by soil type. In other words, it s impossible to give blanket manure application recommendations. They need to be tailored for every situation. We ll start the discussion with dairy cow manure but will also offer information about the handling, characteristics, and uses of some other animal manures. Manure Handling Systems Solid versus Liquid The type of barn on the farmstead frequently determines how manure is handled on a dairy farm. Dairy-cow manure containing a fair amount of bedding, usually around 2% dry matter or higher, is spread as a solid. This is most common on farms where cows are kept in individual stanchions or tie-stalls. Liquid manure-handling systems are common where animals are kept in a free stall barn and minimal bedding is added to the manure. Liquid manure is usually in the range of from 2% to 12% dry matter (88% or more water), with the lower dry matter if water is flushed from alleys and passed through a liquid-solid separator

46 or large amounts of runoff enter the storage lagoon. Manures with characteristics between solid and liquid, with dry matter between 12% and 2%, are usually referred to as semisolid. Composting manures is becoming an increasingly popular option for farmers. By composting manure, you help stabilize nutrients (although considerable ammonium is usually lost in the process), have a smaller amount of material to spread, and have a more pleasant material to spread a big plus if neighbors have complained about manure odors. Although it s easier to compost manure that has been handled as a solid, it does take a lot of bedding to get fresh manure to a 2% solid level. Some farmers are separating the solids from liquid manure and then irrigating with the liquid and composting the solids. Some are separating solids following digestion for methane production and burning the gas to produce electricity or heat. Separating the liquid allows for direct composting of the solids without any added materials. It also allows for easier transport of the solid portion of the manure for sale or to apply to remote fields. For a more detailed discussion of composting, see chapter 13. Some dairy farmers have built what are called compost barns. No, the barns don t compost, but they are set up similar to a free-stall barn, where bedding and manure just build up over the winter and the pack is cleaned out in the fall or spring. However, with composting barns, the manure is stirred or turned twice daily with a modified cultivator on a skid steer loader or small tractor to a depth of 8 to 1 inches; sometimes ceiling fans are used to help aerate and dry the pack during each milking. Some farmers add a little new bedding each day, some do it weekly, and others do it every two to five weeks. In the spring and fall some or all of the bedding can be removed and spread directly or built into a traditional compost pile for finishing. Although farmers using this system tend to be satisfied with it, there is a concern about the continued availability of wood shavings and sawdust for bedding. More recently, vermicomposting has been introduced as a way to process dairy manure. In this case, worms digest the manure, and the castings provide a high-quality soil amendment. Manure from hogs can also be handled in different ways. Farmers raising hogs on a relatively small scale sometimes use hoop houses, frequently placed in fields, with bedding on the floor. The manure mixed with bedding can be spread as a solid manure or composted first. The larger, more industrial-scale farmers mainly use little to no bedding with slatted floors over the manure pit and keep the animals clean by frequently washing the floors. The liquid manure is held in ponds for spreading, mostly in the spring before crops are planted and in the fall after crops have been harvested. Poultry manure is handled with bedding (especially for broiler production) or little to no bedding (industrial-scale egg production). Storage of Manure Researchers have been investigating how best to handle, store, and treat manure to reduce the problems that come with year-round manure spreading. Storage allows the farmer the opportunity to apply manure when it s best for the crop and during appropriate weather conditions. This reduces nutrient loss from the manure, caused by water runoff from the field. However, significant losses of nutrients from stored manure also may occur. One study found that during the year dairy manure stored in uncovered piles lost 3% of the solids, 1% of the nitrogen, 3% of the phosphorus, and 2% of the potassium. Covered piles or wellcontained bottom-loading liquid systems, which tend to form a crust on the surface, do a better job of conserving the nutrients and solids than unprotected piles. Poultry manure, with its high amount of ammonium, may lose 5% of its nitrogen during storage as ammonia gas volatilizes, unless precautions are

47 taken to conserve nitrogen. Regardless of storage method, it is important to understand how potential losses occur in order to select a storage method and location that minimize environmental impact. Chemical Characteristics of Manures A high percentage of the nutrients in feeds passes right through animals and ends up in their manure. Depending on the ration and animal type, over 7% of the nitrogen, 6% of the phosphorus, and 8% of the potassium fed may pass through the animal as manure. These nutrients are available for recycling on cropland. In addition to the nitrogen, phosphorus, and potassium contributions given in table 12.1, manures contain significant amounts of other nutrients, such as calcium, magnesium, and sulfur. For example, in regions that tend to lack the micronutrient zinc, there is rarely any crop deficiency found on soils receiving regular manure applications. The values given in table 12.1 must be viewed with some caution, because the characteristics of manures from even the same type of animal may vary considerably from one farm to another. Differences in feeds, mineral supplements, bedding materials, and storage systems make manure

48 analyses quite variable. Yet as long as feeding, bedding, and storage practices remain relatively stable on a given farm, manure nutrient characteristics will tend to be similar from year to year. However, year-to-year differences in rainfall can affect stored manure through more or less dilution. The major difference among all the manures is that poultry manure is significantly higher in nitrogen and phosphorus than the other manure types. This is partly due to the difference in feeds given poultry versus other farm animals. The relatively high percentage of dry matter in poultry manure is also partly responsible for the higher analyses of certain nutrients when expressed on a wet ton basis. It is possible to take the guesswork out of estimating manure characteristics; most soil-testing laboratories will also analyze manure. Manure analysis should become a routine part of the soil fertility management program on animal-based farms. This is of critical importance for routine manure use. For example, while the average liquid dairy manure is around 25 pounds of N per 1, gallons, there are manures that might be 1 pounds N or less OR 4 pounds N or more per 1, gallons. Recent research efforts have focused on more efficient use of nutrients in dairy cows, and N and P intake can often be reduced by up to 25% without losses in productivity. This helps reduce nutrient surpluses on farms using only needed P. FORMS OF NITROGEN IN MANURES Nitrogen in manure occurs in three main forms: ammonium (NH4 + ), urea (a soluble organic form, easily converted to ammonium), and solid, organic N. Ammonium is readily available to plants, and urea is quickly converted to ammonium in soils. However, while readily available when incorporated in soil, both ammonium and urea are subject to loss as ammonia gas when left on the surface under drying conditions with significant losses occurring within hours of applying to the soil surface. Some manures may have half or three-quarters of their N in readily available forms, while others may have 2% or less in these forms. Manure analysis reports usually contain both ammonium and total N (the difference is mainly organic N), thus indicating how much of the N is readily available but also subject to loss if not handled carefully. Effects of Manuring on Soils Effects on Organic Matter When considering the influence of any residue or organic material on soil organic matter, the key question is how much solids are returned to the soil. Equal amounts of different types of manures will have different effects on soil organic matter levels. Dairy and beef manures contain undigested parts of forages and may have significant quantities of bedding. They therefore have a high amount of complex substances, such as lignin, that do not decompose readily in soils. Using this type of manure results in a much greater long-term influence on soil organic matter than does a poultry or swine manure without bedding. More solids are commonly applied to soil with solid-manure-handling systems than with liquid systems, because greater amounts of bedding are usually included. A number of trends in dairy farming mean that manures may have less organic material than in the past. One is the use of sand as bedding material in free-stall barns, much of which is recovered and reused. The other is the separation of solids and liquids with the sale of solids or the use of digested solids as bedding. Under both situations much less organic solids are returned to fields. On the other hand, the bedded pack (or compost barn) does produce a manure that is high in organic solid content. When conventional tillage is used to grow a crop such as corn silage, whose entire aboveground portion is harvested, research indicates that an annual application of 2 to 3 tons of the solid type of dairy manure per acre is needed to maintain soil organic matter (table 12.2). As discussed above, a nitrogen-demanding

49 crop, such as corn, may be able to use all of the nitrogen in 2 to 3 tons of manure. If more residues are returned to the soil by just harvesting grain, lower rates of manure application will be sufficient to maintain or build up soil organic matter. The Influence of Manure on Many Soil Properties The application of manures causes many soil changes biological, chemical, and physical. A few of these types of changes are indicated in table 12.2, which contains the results of a long-term experiment in Vermont with continuous corn silage on a clay soil. Manure counteracted many of the negative effects of a monoculture cropping system in which few residues are returned to the soil. Soil receiving 2 tons of dairy manure annually (wet weight, including bedding equivalent to approximately 8, pounds of solids) maintained organic matter and CEC levels and close to the original ph (although acid-forming nitrogen fertilizers also were used). Manures, such as from dairy and poultry, have liming effects and actually counteract acidification. (Note: If instead of the solid manure, liquid had been used to supply N and other nutrients for the crop, there would not have been anywhere near as large a beneficial effect on soil organic matter, CEC, and pore space.) High rates of manure addition caused a buildup of both phosphorus and potassium to high levels. Soil in plots receiving manures were better aggregated and less dense and, therefore, had greater amounts of pore space than fields receiving no manure.

50 An example of how a manure addition might balance annual loss is given in figure One Holstein cow year worth of manure is about 2 tons. Although 2 tons of anything is a lot, when considering dairy manure, it translates into a much smaller amount of solids. If the approximately 5,2 pounds of solid material in the 2 tons is applied over the surface of one acre and mixed with the 2 million pounds of soil present to a 6-inch depth, it would raise the soil organic matter by about.3%. However, much of the manure will decompose during the year, so the net effect on soil organic matter will be even less. Let s assume that 75% of the solid matter decomposes during the first year, and the carbon ends up as atmospheric CO2. At the beginning of the following year, only 25% of the original 5,2 pounds, or 1,3 pounds of organic matter, is added to the soil. The net effect is an increase in soil organic matter of.65% (the calculation is [1,3/2,,] x 1). Although this does not seem like much added organic matter, if a soil had 2.17% organic matter and 3% of that was decomposed annually during cropping, the loss would be.65% per year, and the manure addition would just balance that loss. Manures with lower amounts of bedding, although helping maintain organic matter and adding to the active ( dead ) portion, will not have as great an effect as manures containing a lot of bedding material. Using Manures Manures, like other organic residues that decompose easily and rapidly release nutrients, are usually applied to soils in quantities judged to supply sufficient nitrogen for the crop being grown in the current year. It might be better for building and maintaining soil organic matter to apply manure at higher rates, but doing so may cause undesirable nitrate accumulation in leafy crops and excess nitrate leaching to groundwater. High nitrate levels in leafy vegetable crops are undesirable in terms of human health, and the leaves of many plants with high N seem more attractive to insects. In addition, salt damage to crop plants can occur from high manure application rates, especially when there is insufficient leaching by rainfall or irrigation. Very high amounts of added manures, over a period of years, also lead to high soil phosphorus levels (table 12.2). It is a waste of money and resources to add unneeded nutrients to the soil, nutrients that will only be lost by leaching or runoff instead of contributing to crop nutrition. Application Rates A common per-acre rate of dairy-manure application is 1 to 3 tons fresh weight of solid, or 4, to 11, gallons of liquid, manure. These rates will supply approximately 5 to 15 pounds of available nitrogen (not total) per acre, assuming that the solid manure is not too high in straw or sawdust and actually ties up soil nitrogen for a while. If you are growing crops that don t need that much nitrogen, such as small grains, 1 to 15 tons (around 4, to 6, gallons) of solid manure should supply sufficient nitrogen per acre. For a crop that needs a lot of nitrogen, such as corn, 2 to 3 tons (around 8, to 12, gallons) per acre may be necessary to supply its nitrogen needs. Low rates of about 1 tons (around 4, gallons) per acre are also suggested for each of the multiple applications used on a grass hay crop. In total, grass

51 hay crops need at least as much total nitrogen applied as does a corn crop. There has been some discussion about applying manures to legumes. This practice has been discouraged because the legume uses the nitrogen from the manure, and much less nitrogen is fixed from the atmosphere. However, the practice makes sense on intensive animal farms where there can be excess nitrogen although grasses may then be a better choice for manure application. For the most nitrogen benefit to crops, manures should be incorporated into the soil in the spring immediately after spreading on the surface. About half of the total nitrogen in dairy manure comes from the urea in urine that quickly converts to ammonium (NH4 + ). This ammonium represents almost all of the readily available nitrogen present in dairy manure. As materials containing urea or ammonium dry on the soil surface, the ammonium is converted to ammonia gas (NH3) and lost to the atmosphere. If dairy manure stays on the soil surface, about 25% of the nitrogen is lost after one day, and 45% is lost after four days but that 45% of the total represents around 7% of the readily available nitrogen. This problem is significantly lessened if about half an inch of rainfall occurs shortly after manure application, leaching ammonium from the manure into the soil. Leaving manure on the soil surface is also a problem, because runoff waters may carry significant amounts of nutrients from the field. When this happens, crops don t benefit as much from the manure application, and surface waters become polluted. Some liquid manures those with low solids content penetrate the soil more deeply. When applied at normal rates, these manures will not be as prone to lose ammonia by surface drying. However, in humid regions, much of the ammonia-n from manure may be lost if it is incorporated in the fall when no crops are growing. Figure Injection of liquid manure into shallow frozen soils, which eliminates compaction concerns and reduces spring application volumes. Photo by Eleanor Jacobs. Other nutrients contained in manures, in addition to nitrogen, make important contributions to soil fertility. The availability of phosphorus and potassium in manures should be similar to that in commercial fertilizers. (However, some recommendation systems assume that only around 5% of the phosphorus and 9% of the potassium is available.) The phosphorus and potassium contributions contained in 2 tons of dairy manure are approximately equivalent to about 3 to 5 pounds of phosphate and 18 to 2 pounds of potash from fertilizers. The sulfur content as well as trace elements in manure, such as the zinc previously mentioned, also add to the fertility value of this resource. Because one-half of the nitrogen and almost all of the phosphorus is in the solids, a higher proportion of these nutrients remain in sediments at the bottom when a liquid system is emptied without properly agitating the manure. Uniform agitation is recommended if the goal is to apply similar levels of solids and nutrients across target fields. A manure system that allows significant amounts of surface water penetration and then drainage, such as a manure stack of wellbedded dairy or beef cow manure, may lose a lot of potassium because it is so soluble. The 2% leaching loss of potassium from stacked dairy manure mentioned above occurred because potassium was mostly found in the liquid portion of the manure.